The present invention generally relates to radiocommunication systems and, more particularly, to radiocommunication systems which provide for digital voice storage capability in mobile units.
The radiocommunication industry, in particular the cellular telephone industry, has made phenomenal strides in commercial operations in the United States as well as the rest of the world. Growth in major metropolitan areas has far exceeded expectations and is outstripping system capacity. If this trend continues, the effects of rapid growth will soon reach even the smallest markets. Innovative solutions are required to meet these increasing capacity needs as well as maintain high quality service and avoid rising prices.
Throughout the world, one important step in cellular systems is to change from analog to digital transmission. Equally important is the choice of an effective digital transmission scheme for implementing the next generation cellular technology. Furthermore, it is widely believed that the first generation of Personal Communication Networks (PCNs), employing low cost, pocket-size, cordless telephones that can be carried comfortably and used to make or receive calls in the home, office, street, car, etc., will be provided by cellular carders using the next generation digital cellular system infrastructure.
As users become accustomed to communicating using a portable or hand-held device, they will expect these devices to provide all of the additional features which they enjoy in more traditional, line-bound telephone systems. Thus, features such as call forwarding and conference calling are being implemented in radiocommunication systems.
Users are also accustomed to having message storage and retrieval capabilities associated with their telephone systems. This capability is provided in line-bound systems by, for example, answering machines and voice mail systems. Answering machines, which typically use electromechanical storage devices that are bulky and complex, are not very practical for portable communication devices. Voice mail type systems, which are essentially central repositories for stored messages, have been used in paging systems but are not optimal for radio communication devices which are not always connected to the system.
Because of the many drawbacks of conventional message storage and retrieval systems vis-a-vis radio communication systems, many of today's cellular systems have no message storing capability whatsoever. These systems simply play a standard message informing a caller that the person whom they are trying to reach cannot be reached at that time. This frustrates users who must then continually redial the person whom they are trying to contact.
There have been attempts in the prior art to provide message storage and retrieval capability to mobile phones in radiocommunication systems. For example, U.S. Pat. No. 4,495,647 to Burke et al. discloses a digital voice storage mobile in which a mobile unit has up to eight 64K dynamic RAMs which can store up to 42 seconds of speech. The messages are digitized using CVSD circuitry. However, this approach is problematic in that Burke et al simply digitizes the incoming and outgoing messages without data compression. Lacking data compression, this system must either provide more memory to store the desired amount of voice data or accept less voice data storage.
U.S. Pat. No. 5,003,576 to Helferich discloses an analog/digital voice storage cellular phone in which messages can be transmitted to the mobile at a high rate and replayed later by the user at a slower rate. Much like the Burke system, however, the system of Helferich simply digitizes the incoming messages and stores them in memory without data compression and, therefore, suffers from the same drawbacks as set forth above.
U.S. Pat. No. 5,105,197 to Clagett discloses a system wherein messages are stored in stationary sites and transmitted to mobile units using data compression to conserve resources, i.e., both spectrum and memory. Since the messages are not stored at the mobile unit, the user must wait until she or he is within range of the stationary site which stores her or his messages which can be very frustrating for someone who wishes to access their messages when they are not in range of the appropriate stationary site.
From the foregoing, it can be seen that the need exists for a mobile unit which can provide local voice storage using data compression, but without adding additional, expensive circuitry or changing existing standards.